Testing for checking the accuracy (i.e., calibration) of a liquid flowmeter is generally carried out using a weighing or volume method compliant with Japanese Industrial Standards JIS B 7552 (see “Procedures for calibration and testing for liquid flowmeter”, JIS B 7552, Japanese Industrial Standards). For example, as a way to achieve high-accuracy calibration, a liquid passage type weighing method is known, which measures the flow rate of a test liquid by introducing the test liquid through a flow generating device (e.g., pump) into a flowmeter under test, and discharging the test liquid passed through the flowmeter into a weighing tank using a diverter for only a predetermined period of time.